DOC: Add the non-local mean denoising procedure in DKI sample of usage script
DOC: Add the non-local mean denoising procedure in DKI sample of usage script

FrancoisRheaultUS/dipy,JohnGriffiths/dipy,nilgoyyou/dipy,StongeEtienne/dipy,demianw/dipy,nilgoyyou/dipy,StongeEtienne/dipy,matthieudumont/dipy,matthieudumont/dipy,demianw/dipy,FrancoisRheaultUS/dipy,villalonreina/dipy,villalonreina/dipy,JohnGriffiths/dipy